SAN FRANCISCO— The world’s climate crisis has hit a dire new milestone: The extent of sea ice across the Arctic is the smallest on record, the National Snow and Ice Data Center announced today. The agency said sea ice currently covers just 1.58 million square miles (4.1 million square kilometers).

“This is a profound — and profoundly depressing — moment in the history of our planet,” said Shaye Wolf, climate science director at the Center for Biological Diversity’s Climate Law Institute. “The sea-ice death spiral, coming during one of the warmest summers in American history, is just one more clear sign of the deepening climate crisis that we ignore at our own peril.”

The previous minimum since satellite records began in 1972 was 1.61 million square miles (4.17 million square kilometers) on Sept. 18, 2007, according to the National Snow and Ice Data Center. The record was broken this year several weeks before the minimum extent is normally reached, and additional sea-ice declines are very likely since the ice may continue to decline through mid-September. The current sea ice extent is about 1.1 million square miles less than the average minimum extent between 1979 and 2000 – that’s like losing an area of ice one-third the size of the contiguous United States.

Arctic sea ice plays a critical role in regulating our global climate by reflecting most of the sun’s energy back into space and keeping the polar region cool. As the ice pack melts, more of the sun’s energy is absorbed by the underlying seawater, spurring the Arctic to heat up at an ever-faster pace. Recent studies have linked melting sea ice and accelerating Arctic warming to changes in the Jet Stream that increase the frequency of extreme weather events such as droughts, floods, heat waves and cold spells in the United States and other mid-latitude regions of the Northern Hemisphere.

The rapid loss of sea ice also poses a severe threat to endangered polar bears, ice seals, walruses and other Arctic animals that rely on sea ice for survival.

“Polar bears, seals and other Arctic wildlife will bear the deadly brunt of ice loss, but all of us will be hurt by the world’s quickly warming climate if we don’t act now,” Wolf said.

Today’s announcement caps a summer of record-breaking extreme weather events fueled by manmade climate change. Since Jan. 1, 2012, more than 40,000 high temperature records have been broken in the United States, according to the National Oceanic and Atmospheric Administration. At the end of July, the hottest month on record, approximately two-thirds of the country was in drought.

In addition to the loss of sea-ice extent, the thickness and volume of the ice has also been declining dramatically, making the overall ice pack more vulnerable to further summer melting. Earlier this month, researchers with the European Space Agency’s CryoSat-2 probe reported that Arctic sea-ice volume is declining much faster than expected, with 3,118 cubic miles (13,000 cubic kilometers) of sea ice measured in the summer of 2004 and only 1,679 cubic miles (7,000 cubic kilometers) this summer. At the current pace, the Arctic could be ice-free in the summer for a day or more by the end of the decade. Animals that rely on the sea ice for hunting, resting and raising young are almost certain to face a higher death toll from starvation and drowning.

Greenland also experienced record melting this summer, with a record 97 percent of the ice sheet undergoing surface melting on July 15, 2012, according to NASA. The melting of the land-based Greenland ice sheet raises sea levels and threatens coastal communities around the globe.

“Deep and rapid carbon pollution cuts are essential to slow the warming of the Arctic and maintain a safe climate for the rest of the globe,” said Wolf. “Reductions in the powerful greenhouse pollutants methane and black carbon are also needed to slow warming in the short term.”

Both the technology and the legal tools to achieve rapid greenhouse pollution reductions are already in place. Full use of all of the Clean Air Act’s successful pollution-reduction programs is our best route to quick reductions in greenhouse gas emissions. The Obama administration, however, has been too slow and timid in using the law to cut pollution. In response, 34 communities representing more than 13 million people have joined the Center’s Clean Air Cities campaign, which urges President Obama and the EPA to address the climate crisis through the Clean Air Act’s science-based programs.

The Center for Biological Diversity is a national, nonprofit conservation organization with more than 375,000 members and online activists dedicated to the protection of endangered species and wild places.